Flag Day will be celebrated on June 14 this year as it is every year. Although it is not a federal holiday, it is a national observance—a celebration of an event but not usually a day off from work.
June 14 is the anniversary of the day the Second Continental Congress passed a resolution in 1777 declaring that the United States flag would be 13 stripes that alternated red and white, and there would be 13 white stars in a blue field. Prior to that each colony had its own flag.
The 13 white stars represented the original 13 colonies. New stars were added as states joined the union. July 4, 1960, was the first time that the 50-star flag was flown. This followed Alaska joining as the 49th and Hawaii joining as the 50th state in 1959.
If you plan to fly the flag and need guidance on the rules for displaying the flag, here is a site that can help you.